{
  "abstract": "Introduction Heart disease (HD) contributes to 32% of all deaths annually, yet therapy options remain limited. Adverse cardiac remodelling (ACR) underpins HD, but the role of the tissue microenvironment in regulating the cells responsible for matrix homeostasis, cardiac fibroblasts (CFs), remains largely unknown. The microenvironment of the cardiac stromal tissue is complex, with both mechanical and chemical factors influencing resident cells. CFs sense damaged tissue during ischemia by detecting changes in chemical and mechanical signals. This response can be both anabolic and catabolic, with problems arising when CFs fail to resolve their response, leading to fibrosis or ACR, respectively. Acidic pH is known to play a major role in cardiomyocyte injury, but its effects on CFs remain unclear. Furthermore, CFs are known to be mechanoresponsive, but the combination of mechano-chemical signalling has not been characterised.The aim was to assess the homeostatic matrix response of CFs to changes in mechanical strain, pH and TGFβ1, mimicking the mechano-chemical microenvironment of healthy and diseased myocardium.Materials and Methods An immortalised human CF cell line (n=3) was cultured for 3 days +/- TGFβ1, at pH 7.4, 7.1 and 6.8 (mimicking healthy and diseased myocardium) and stimulated +/- cyclic tensile strain (CTS) (10% strain, 1.0Hz, 3 days) using a Flex Jr.™ Tension System. qRT-PCR was used to assess the gene expression of matrix homeostatic markers (COLI/III, aSMA, FN1, MMPs and TIMPs). Immunofluorescence imaging was used to assess the expression levels of aSMA protein, YAP localisation and chromatin structure.Results/Discussion The response of CFs to decreases in pH was gene-specific, with pH 6.8 causing downregulation of COL3, TNC, MMP9 and upregulation of MMP3, suggesting a complex matrix remodelling response ( figure 1). Administration of CTS upregulated the expression of COL3 and TNC in a pH-dependent manner, with COL3 responsive to CTS at pH 7.4 and 6.8, but TNC only responsive at pH 7.4 (figure 1). TMIP1 and CTGF showed insensitivity to pH when unstrained; however, addition of CTS upregulated both genes at pH 6.8 only, suggesting acidic pH promoted a pro-fibrotic response in CFs to mechanical stretch. CFs responded to TGFβ1 by increasing fibrotic markers. We observed a pH-dependent TGF-β1 response in TIMP1 and LOX, with these genes responding only to TGF-β1 at acidic pH, again suggesting that acidic pH promotes fibrotic phenotypes. A coactive effect was observed for COL3 when TGF-β1 and CTS were combined (figure 2).These novel results highlight crosstalk among pH, CTS, and TGF-β1 signalling pathways, suggesting that CF physiological responses to ischemia-induced acidosis may differ depending on myocardial dynamics.Future experiments aim to reveal the mechano-chemically signalling pathways underpinning this observation, focusing on ion channel involvement and intracellular pH homeostasis. Better understanding of mechano-chemical signalling pathways may identify novel therapeutic targets for HD.",
  "authors": [
    {
      "affiliations": [
        "Keele University, Stoke-on-Trent, United Kingdom"
      ],
      "name": "Daniel Salazar Lopez"
    },
    {
      "affiliations": [
        "Keele University, Stoke-on-Trent, United Kingdom"
      ],
      "name": "Alan Harper"
    },
    {
      "affiliations": [
        "Keele University, Stoke-on-Trent, United Kingdom"
      ],
      "name": "Ying Yang"
    },
    {
      "affiliations": [
        "Keele University, Stoke-on-Trent, United Kingdom"
      ],
      "name": "Mamas Mamas"
    },
    {
      "affiliations": [
        "Keele University, Stoke-on-Trent, United Kingdom",
        "Manchester University, Manchester, United Kingdom"
      ],
      "name": "Hamish Gilbert"
    }
  ],
  "title": "324 The response of human cardiac fibroblasts to cyclic tensile strain is pH- and TGFβ1-dependent",
  "uid": "19822d76-72ca-527b-b24f-4a945730bb24"
}